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Re^4: Loading a part of the file to array using Tie::File

by karlgoethebier (Abbot)
on Nov 24, 2017 at 09:27 UTC ( #1204193=note: print w/replies, xml ) Need Help??


in reply to Re^3: Loading a part of the file to array using Tie::File
in thread Loading a part of the file to array using Tie::File

Thanks ikegami.

But this is a rigorous verdict which marks Tie::File as unusable and not recommendable, right?

Or do you see any serious use cases for it?

Best regards, Karl

«The Crux of the Biscuit is the Apostrophe»

perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'Help

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Re^5: Loading a part of the file to array using Tie::File
by haukex (Bishop) on Nov 24, 2017 at 19:10 UTC
    Or do you see any serious use cases for it?

    Dunno, I think that for random access of small files (say, maybe, under a megabyte) in situations where performance is not critical, the ease of implementation can still outweigh the cost. On the other hand, at least in my experience such files are rare. For example, when inserting lines somewhere, one usually has to scan the file to locate the insertion point anyway, so in such cases a while(<>) loop would still feel more natural to me than a linear search in an array. It's maybe a nice module to show off some of the power (Update: as in expressiveness / TIMTOWTDI, not speed) of Perl to newcomers, although then one might cause the problem of "if all you have is a hammer, everything looks like a nail".

    Of course ikegami has a good point. There is a huge difference between reading even a ~1MB file into in array, vs. reading it with Tie::File:

    $ cp -L /usr/share/dict/words /tmp/test.txt $ wc -l /tmp/test.txt 99132 /tmp/test.txt $ du -sh /tmp/test.txt 920K /tmp/test.txt $ time perl -MTie::File -e 'open F, "/tmp/test.txt" or die; print `ps -orss $$`; my @x = <F>; print `ps -orss $$`' RSS 7408 RSS 23604 real 0m0.042s user 0m0.024s sys 0m0.012s $ time perl -MTie::File -e 'tie my @a, "Tie::File", "/tmp/test.txt"; print `ps -orss $$`; $a=$_ for @a; print `ps -orss $$`' RSS 7612 RSS 55024 real 0m1.001s user 0m0.908s sys 0m0.088s

      Dunno, I think that for random access of small files (say, maybe, under a megabyte) in situations where performance is not critical, the ease of implementation can still outweigh the cost

      Except it's just as easy to load the file into memory and write it back out when it's that small.

        Except it's just as easy to load the file into memory and write it back out when it's that small.

        By "ease of implementation" I meant:

        open my $ifh, '<', $file or die $!; chomp( my @a = <$ifh> ); close $ifh; # vs. use Tie::File; tie my @a, 'Tie::File', $file; # and open my $ofh, '>', $file or die $!; print $ofh $_,"\n" for @a; close $ofh; # vs. untie @a;

        I think several arguments, some subjective, could be made in either direction which one "easier". Whether it's worth the cost (speed and memory penalty) depends on the application, and of course the user must be aware of the penalty in the first place, so it's definitely good to caution. I just personally wouldn't reject the module outright.

        Granted, if it's about reducing the length of the code, it's also possible to do something like this, although it still has a speed penalty, just not quite as bad as Tie::File:

        use Path::Class qw/file/; my @a = file($file)->slurp(chomp=>1); ... file($file)->spew_lines(\@a);

        A while(<>) should still be faster than any of the above. (I ran some quick back-of-the-envelope benchmarks with /usr/share/dict/words.)

        Karl asked about "serious" use cases. Under the conditions I named, I'd say it's just a matter of TIMTOWTDI, but if you were to say that's not a "serious" use case, then you wouldn't be wrong. I think I'll be cautioning against Tie::File more in the future.

      Thank you very much for advice haukex. But to be honest: I struggle a bit about what you benchmarked. I guess i need to take a closer look at your results ;-) Best regards, Karl

      «The Crux of the Biscuit is the Apostrophe»

      perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'Help

      Didnt you look at the benchmark?
Re^5: Loading a part of the file to array using Tie::File
by ikegami (Patriarch) on Nov 24, 2017 at 17:17 UTC

    Or do you see any serious use cases for it?

    I do not. Let's revisit my first words on this: "First of all, you don't want Tie::File. You never want Tie::File."

      Thank you very much for advice ikegami. Best regards, Karl

      «The Crux of the Biscuit is the Apostrophe»

      perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'Help

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